Database and Application Security

Database and Application Security
S. Sudarshan Computer Science and Engg. Dept I.I.T. Bombay Database and Application Security, Nov 2006

Database and Application Security, Nov 2006
Database Security Database Security - protection from malicious attempts to steal (view) or modify data. Database and Application Security, Nov 2006

Importance of Data Bank/Demat accounts Credit card, Salary, Income tax data University admissions, marks/grades Land records, licenses Data = crown jewels for organizations Recent headlines: Personal information of millions of credit card users stolen Laws on privacy in the US Theft of US data in India Criminal gangs get into identity theft Earlier this year in Mumbai Hackers steal credit card data using card reader and make fraudulent purchases Hacker creates fake Web site to phish for credit card information Auto-rickshaw license fraud in New Delhi Database and Application Security, Nov 2006

Identity Theft Pretend to be someone else and get credit cards/loans in their name Identification based on “private” information that is not hard to obtain online More lucrative than blue-collar crime, harder to catch criminals Hurts victims even more than regular theft Onus goes on innocent people to prove they didn’t get loans or make credit card payment Credit history gets spoilt, making it harder to get future loans And you may have been robbed without ever knowing about it. Increasing risk in India PAN numbers, names available online Database and Application Security, Nov 2006

What me worry? “Bad things only happen to other people.”?? SQL/Slammer Attacked SQLServer, brought networks down all over the world (including IITB) Luckily no data lost/stolen Flaw in registration script at database security workshop at IIT Bombay Careless coding exposed database password to outside world Most Web applications vulnerable to SQL injection attacks Database and Application Security, Nov 2006

Overview Levels of data security Authorization in databases Application Vulnerabilities Summary and References Database and Application Security, Nov 2006

Levels of Data Security
Human level: Corrupt/careless User Network/User Interface Database application program Database system Operating System Physical level Database and Application Security, Nov 2006

Physical/OS Security Physical level Traditional lock-and-key security Protection from floods, fire, etc. E.g. WTC (9/11), fires in IITM, WWW conf website, etc. Protection from administrator error E.g. delete critical files Solution Remote backup for disaster recovery Plus archival backup (e.g. DVDs/tapes) Operating system level Protection from virus/worm attacks critical Database and Application Security, Nov 2006

Database Encryption E.g. What if a laptop/disk/USB key with critical data is lost? Partial solution: encrypt the database at storage level, transparent to application Whole database/file/relation Unit of encryption: page Column encryption Main issue: key management E.g. user provides decryption key (password) when database is started up Supported by many database systems Standard practice now to encrypt credit card information, and other sensitive information Database and Application Security, Nov 2006

Security (Cont.) Network level: must use encryption to prevent Eavesdropping: unauthorized reading of messages Masquerading: pretending to be an authorized user or legitimate site, or sending messages supposedly from authorized users Database and Application Security, Nov 2006

Network Security All information must be encrypted to prevent eavesdropping Public/private key encryption widely used Handled by secure http Must prevent person-in-the-middle attacks E.g. someone impersonates seller or bank/credit card company and fools buyer into revealing information Encrypting messages alone doesn’t solve this problem More on this in next slide Database and Application Security, Nov 2006

Site Authentication Digital certificates are used in https to prevent impersonation/man-in-the middle attack Certification agency creates digital certificate by encrypting, e.g., site’s public key using its own private key Verifies site identity by external means first! Site sends certificate to buyer Customer uses public key of certification agency to decrypt certificate and find sites public key Man-in-the-middle cannot send fake public key Sites public key used for setting up secure communication Database and Application Security, Nov 2006

Security at the Database/Application Program
Authentication and authorization mechanisms to allow specific users access only to required data Authentication: who are you? Prove it! Authorization: what you are allowed to do Database and Application Security, Nov 2006

Database vs. Application
Application authenticates/authorizes users Application itself authenticates itself to database Database password Application Program Database Database and Application Security, Nov 2006

User Authentication Password Most users abuse passwords. For e.g. Easy to guess password Share passwords with others Smartcards Need smartcard + a PIN or password Bill Gates Database and Application Security, Nov 2006

User Authentication Central authentication systems allow users to be authenticated centrally LDAP or MS Active Directory often used for central authentication and user management in organizations Single sign-on: authenticate once, and access multiple applications without fresh authentication Microsoft passport, PubCookie etc Avoids plethora of passwords Password only given to central site, not to applications Database and Application Security, Nov 2006

Overview Levels of security Authorization in databases Application Vulnerabilities References Database and Application Security, Nov 2006

Authorization Different authorizations for different users Accounts clerk vs. Accounts manager vs. End users Database and Application Security, Nov 2006

Database/Application Security
Ensure that only authenticated users can access the system And can access (read/update) only data/interfaces that they are authorized to access Database and Application Security, Nov 2006

Limitations of SQL Authorization
SQL does not support authorization at a tuple level E.g. we cannot restrict students to see only (the tuples storing) their own grades Web applications are dominant users of databases Application end users don't have database user ids, they are all mapped to the same database user id Database access control provides only a very coarse application-level access control Database and Application Security, Nov 2006

Access Control in Application Layer
Applications authenticate end users and decide what interfaces to give to whom Screen level authorization: which users are allowed to access which screens Parameter checking: users only authorized to execute forms with certain parameter values E.g. CSE faculty can see only CSE grades Database and Application Security, Nov 2006

Access Control in Application Layer
Authorization in application layer vs. database layer Benefits fine grained authorizations, such as to individual tuples, can be implemented by the application. authorizations based on business logic easier to code at application level Drawback: Authorization must be done in application code, and may be dispersed all over an application Hard to check or modify authorizations Checking for absence of authorization loopholes becomes very difficult since it requires reading large amounts of application code Need a good via-media Database and Application Security, Nov 2006

Oracle Virtual Private Database
Oracle VPD Provides ability to automatically add predicates to where clause of SQL queries, to enforce fine-grained access control E.g. select * from grades becomes select * from grades where rollno=userId() Mechanism: DBA creates an authorization function. When invoked with a relation name and mode of access, function returns a string containing authorization predicate Strings for each relation and-ed together and added to user’s query Application domain: hosted applications, where applications of different organizations share a database (down to relation level) Added predicates ensures each organization sees only its own data Database and Application Security, Nov 2006

Privacy Aggregate information about private information can be very valuable E.g. identification of epidemics, mining for patterns (e.g. disease causes) etc. Privacy preserving data release E.g. in US, many organizations released “anonymized” medical data, with names removed, but zipcode (= pincode), sex and date of birth retained Turns out above (zipcode,sex,date of birth) uniquely identify most people! Correlate anonymized data with (say) electoral data with same information Recent problems at America Online Released search history, apparently anonymized, but users could be easily identified in several cases Several top officials were fired Earlier problems revealed medical history of Massachusetts state governer. Not yet a criminal issue, but lawsuits have happened Conflict with Right To Information Act Many issues still to be resolved Database and Application Security, Nov 2006

Overview Levels of security Authorization in databases Application Vulnerabilities References Database and Application Security, Nov 2006

Applications are often the biggest source of insecurity Poor coding of application may allow unauthorized access Application code may be very big, easy to make mistakes and leave security holes Very large surface area Used in fewer places Some security by obfuscation Lots of holes due to poor/hasty programming Database and Application Security, Nov 2006

OWASP Top 10 Web Security Vulnerabilities
Unvalidated input Broken access control Broken account/session management Cross-site scripting (XSS) flaws Buffer overflows (SQL) Injection flaws Improper error handling Insecure storage Denial-of-service Insecure configuration management Database and Application Security, Nov 2006

SQL Injection E.g. application takes accnt_number as input from user and creates an SQL query as follows: string query = "select balance from account where account_number =‘" + accnt_number +"‘" Suppose instead of a valid account number, user types in ‘; delete from r; then (oops!) the query becomes select balance from account where account_number =‘ ‘; delete from r; Hackers can probe for SQL injection vulnerability by typing, e.g. ‘*** in an input box Tools can probe for vulnerability Error messages can reveal information to hacker Database and Application Security, Nov 2006

Preventing SQL Injection
To prevent SQL injection attacks use prepared statements (instead of creating query strings from input parameters) PreparedStatement pstmt= conn.prepareStatement( "select balance from account where account_number =?“); pstmt.setString(1,accnt_number); pstmt.execute(); (assume that conn is an already open connection to the database) Alternatives: use stored procedures use a function that removes special characters (such as quotes) from strings Database and Application Security, Nov 2006

Passwords in Scripts E.g.: file1.jsp (or java or other source file) located in publicly accessible area of web server Intruder looks for or .jsp.swp, etc If jsp has database userid/password in clear text, big trouble Happened at IITB Morals Never store scripts (java/jsp) in an area accessible to http Never store passwords in scripts, keep them in config files Never store config files in any web-accessible areas Restrict database access to only trusted clients At port level, or using database provided functionality Database and Application Security, Nov 2006

Outsider vs. Insider Attack
Most security schemes address outsider attack Have password to database? Can update anything Bypassing all application level security measures More people with access  more danger Application program has database password Great deal of trust in people who manage databases Risk of compromise greater with value of data Happened with auto-rickshaw registration in New Delhi Database and Application Security, Nov 2006

Protecting from Users Multi-person approval: Standard practice in banks, accounts departments Encoded as part of application workflow External paper trail Strong authentication of users Smart cards Careful allocation of authorizations on a need to use basis Practical problem: absence of a user should not prevent organization from functioning Many organizations therefore grant overly generous authorizations Database and Application Security, Nov 2006

Protecting from Programmers/DBA
Have password to database, can update anything! Digital signatures by end users can help in some situations E.g. low update rate data such as land records, birth/death data Application program has database password Seize control of the application program  can do anything to the database Solution: Don’t give database password to development team keep password in a configuration file on live server, accessible to only a few system administrators Ongoing research on trusted applications E.g. OS computes checksum on application to verify corruption Allows file-system access only to trusted applications Database and Application Security, Nov 2006

Protection from admin/super-users
Operating system administrators (also known as super-users) can do anything they want to the database. Small number of trusted administrators What if a laptop with critical data is lost? Encrypt entire database (and/or file system) Supported, e.g. in SQL Server 2005 Authentication (password/smart card) when database is started up Database and Application Security, Nov 2006

Detecting Corruption Audit trails: record of all (update) activity on the database: who did what, when Application level audit trail Helps detect fraudulent activities by users Independent audit section to check all updates BUT: DBAs can bypass this level E.g. audit trail apparently deleted in New Delhi auto-rickshaw license case by malicious users with DBA access Database level audit trail Database needs to ensure these can’t be turned off, and turned on again after doing damage Supported by most commercial database systems But required DBAs with knowledge of application to monitor at this level Keep archival copies and cross check periodically Database and Application Security, Nov 2006

So you thought only the query result matters?
Information Leakage So you thought only the query result matters? Database and Application Security, Nov 2006

Information Leakage via UDFs
Auth view myemployee: only those employee whose dept_id is in A1 Query: select * from employee where myudf(salary) Final query plan is not safe UDF may be pushed down in plan, and executed on unauthorized intermediate result As a side-effect, UDF may expose values passed to it [Litchfield] Can be partly solved using sandboxing σmyudf(E.salary) employees A1 σmyudf(E.salary) employees A1 σmyudf(E.salary) myemployees Database and Application Security, Nov 2006

Other channels of information leakage
Exceptions, Error Messages Query: select * from employee where 1/(salary-100K) = 0.23 Query plan: Selection condition in query gets pushed below authorization semi-join Divide by zero exception if salary = 100K Reveals that employee has salary = 100K Timing Analysis Sub-query can perform an expensive computation only if certain tuples are present in its input To prevent leakage, treat all channels as unsafe operations Database and Application Security, Nov 2006

Preventing Information Leakage via UDFs
UDF on Top: Keep UDFs at the top of query plan Definitely safe, no information leakage Better plans possible if UDF is selective Optimal Safe plan When is a plan safe? How to search for optimal safe plan? For details, see: Kabra et al., SIGMOD 2006 σmyudf(E.salary) employees A1 σmyudf(E.salary) employees A1 While UDFonTop obviously prevents information leakage via UDFs, we are not satisfied. We are now thinking is that the cheapest plan for this query? Probably not. If UDF happens to be very selective, keeping the UDF on top is not the best choice. Therefore, we now want to find the optimal safe plan. For this, we need to first characterize when is a query plan safe? In other words, how do we know if the UDF placement in a certain alternative plan cannot leak any information? Once we define the space of plans that are guaranteed to be safe with respect to UDFs, we would like to modify the existing Optimizer to search for an optimal plan within this search space. Database and Application Security, Nov 2006

Overview Levels of security Authorization in databases Application Vulnerabilities Summary Database and Application Security, Nov 2006

Summary Data security is critical Requires security at different levels Several technical solutions But human training is essential Database and Application Security, Nov 2006

Acknowledgments Pictures in this talk stolen from various web sources! Database and Application Security, Nov 2006

References (Shameless advertisement!) Chapter 8 of Database System Concepts 5th Edition, Silberschatz, Korth and Sudarshan, McGraw-Hill The Open Web Application Security Project Web application security scanners e.g. WebInspect (SPI Dynamics) SQL Injection 9 ways to hack a web app Related research papers Kabra, Ramamurthy and Sudarshan, Redundancy and Information Leakage in Fine-Grained Access Control, SIGMOD 2006 Rizvi, Mendelzon, Sudarshan and Roy, Extending Query Rewriting Techniques for Fine-Grained Access Control, SIGMOD 2004 Database and Application Security, Nov 2006

Extra Slides Database and Application Security, Nov 2006

Authorization Forms of authorization on (parts of) the database: Read authorization - allows reading, but not modification of data. Insert authorization - allows insertion of new data, but not modification of existing data. Update authorization - allows modification, but not deletion of data. Delete authorization - allows deletion of data Database and Application Security, Nov 2006

Security Specification in SQL
The grant statement is used to confer authorization grant <privilege list> on <relation name or view name> to <user list> <user list> is: a user-id public, which allows all valid users the privilege granted A role (more on this later) Granting a privilege on a view does not imply granting any privileges on the underlying relations. The grantor of the privilege must already hold the privilege on the specified item (or be the database administrator). Database and Application Security, Nov 2006

Privileges in SQL select: allows read access to relation,or the ability to query using the view Example: grant users U1, U2, and U3 select authorization on the branch relation: grant select on branch to U1, U2, U3 insert: the ability to insert tuples update: the ability to update using the SQL update statement delete: the ability to delete tuples. references: ability to declare foreign keys when creating relations. usage: In SQL-92; authorizes a user to use a specified domain all privileges: used as a short form for all the allowable privileges Database and Application Security, Nov 2006

Privilege To Grant Privileges
with grant option: allows a user who is granted a privilege to pass the privilege on to other users. Example: grant select on branch to U1 with grant option gives U1 the select privileges on branch and allows U1 to grant this privilege to others Database and Application Security, Nov 2006

Roles Roles permit common privileges for a class of users can be specified just once by creating a corresponding “role” Privileges can be granted to or revoked from roles Roles can be assigned to users, and even to other roles SQL:1999 supports roles create role teller create role manager grant select on branch to teller grant update (balance) on account to teller grant all privileges on account to manager grant teller to manager grant teller to alice, bob grant manager to avi Database and Application Security, Nov 2006

Revoking Authorization in SQL
The revoke statement is used to revoke authorization. revoke<privilege list> on <relation name or view name> from <user list> [restrict|cascade] Example: revoke select on branch from U1, U2, U3 cascade Revocation of a privilege from a user may cause other users also to lose that privilege; referred to as cascading of the revoke. We can prevent cascading by specifying restrict: revoke select on branch from U1, U2, U3 restrict With restrict, the revoke command fails if cascading revokes are required. Database and Application Security, Nov 2006

Revoking Authorization in SQL (Cont.)
<privilege-list> may be all to revoke all privileges the revokee may hold. If <revokee-list> includes public all users lose the privilege except those granted it explicitly. If the same privilege was granted twice to the same user by different grantees, the user may retain the privilege after the revocation. All privileges that depend on the privilege being revoked are also revoked. Database and Application Security, Nov 2006

Secure Payment Three-way communication between seller, buyer and credit-card company to make payment Credit card company credits amount to seller Credit card company consolidates all payments from a buyer and collects them together E.g. via buyer’s bank through physical/electronic check payment Several secure payment protocols E.g. Secure Electronic Transaction (SET) Database and Application Security, Nov 2006

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